secret-sharing/src/churp/dealer: Limit loop for polynomial generation

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 65.20%. Comparing base (95d47b5) to head (30aa3e2). Report is 25 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5914 +/- ## ========================================== + Coverage 64.74% 65.20% +0.45% ========================================== Files 627 627 Lines 64292 64292 ========================================== + Hits 41627 41920 +293 + Misses 17756 17459 -297 - Partials 4909 4913 +4 ```

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